The present invention relates generally to the fabrication and installation of wooden hand rails for freeform staircases, such as spiral staircases, and more particularly relates to improved clamping methods and apparatus for fabricating and installing curved, laminated wooden staircase hand rails.
As is well known in the construction industry, the fabrication and installation of curved, laminated wooden hand rails on curving staircase structures is a cumbersome, time-consuming and rather difficult task which must be carefully performed in order to provide an acceptable installed hand rail product. The typical spiral staircase hand rail is formed from an elongated, laminated wooden structure commonly referred to as a "bending rail" which is defined by a laterally abutting series of relatively thin flexible wooden laminae which are glued together to form the hand rail which typically is provided with an ornately configured cross-section along its length, the decorative cross-section usually having lateral projections and indentations along its length.
To form the wooden bending rail, a suitable wood glue is applied to the facing vertical side surfaces of the individual laminae, and the laminae are then hand-pressed and held together until the initially assembled bending rail is clamped to temporary vertical support members secured to each individual stair step on the stair case. Since conventional bending rails are quite long-typically in the range of from about 16 feet to about 30 feet--it normally takes four or five workers to manually hold spaced apart longitudinal sections of the bending rail together until the rail is temporarily clamped to these vertical support members. The four or five workers typically carry the bending rail up the staircase, while still holding the individual rail laminae together, and a central longitudinal portion of the rail is clamped to one of the vertical support members. The rail is then bent into place and successively clamped (toward its opposite ends) to additional temporary vertical support members.
Additional intermediate clamps are then installed on the bending rail, between each of the vertical support members, and the glue between the rail laminae is allowed to dry. When the glue has dried, the temporary clamps are removed, and the bending rail is permanently secured to balusters later installed on the staircase.
In addition to being a decidedly awkward task, this conventional installation of wooden bending rails is less than satisfactory from a variety of other standpoints. For example, the temporary clamping of longitudinally spaced apart sections of the bending rail is conventionally accomplished using ordinary metal C-clamps which force small wooden blocks against opposite, laterally outwardly projecting side surface portions of the rail. This causes undesirable lateral stress concentrations on the outwardly projecting opposite side portions of the rail, tending to indent and mar them. Accordingly, when the temporary clamps are removed, a great deal of work is often required to smooth over these marred areas.
Additionally, to inhibit relative vertical shifting between the individual rail laminae, it has heretofore been necessary to form complementary ribs and grooves on the vertical side surfaces of the laminae which are adapted to interlock and hold the upper and lower side surfaces of the rail in precise alignment while the laminae are being manually pressed together by the various workers as the rail is being carried up the staircase and being temporarily clamped to the vertical support members. The necessity of forming these interlocking ribs and grooves on the individual bending rail laminae significantly increases the fabrication cost of the bending rail. Moreover, it is necessary that these interlocking ribs and grooves be very precisely located on the individual laminae to avoid undesirable irregularities in the top and bottom side surfaces of the bending rail. If these ribs and grooves are not very precisely located, it is necessary to subsequently expend considerable effort to smooth out the top and bottom side surfaces of the finished bending rail.
From the foregoing it can be readily seen that improved clamping apparatus and methods for forming and installing bending rails of this general type would be highly desirable. It is accordingly an object of the present invention to provide such improved apparatus and methods.